Valve Control - Process Pressure and Standard Pressure

something to do with areas maybe?

What you have is two different specs on the valve. The 300 psi is max pressure rating of the valve. The 3-15 psi is the pressure needed to the pneumatically actuated port to shift the spool in the valve. The actuation pressure will vary between 3-15 psi depending on what the pressure is at the valve body inlet port.

Compare the area of your actuator's diaphragm and the area of the valve's plug.

Let's say your valve plug is 1 sq. in. and your diaphragm is 255 sq. in. 300 psi on your 1 sq.in. plug is 300 pounds. 15 psi on your diaphragm's 255 sq.in. is 3,825 pounds. The diaphragm, therefore, has more force to push or pull the valve plug even when 300 psi is acting on it.

regards,

Vulcan

Interesting,

But can you please show it mathematically and step by step.

It depends upon the specific design of the valve, so it is not possible to describe it mathematically without focussing on a particular valve. Vulcan's description is satisfactory.

Valve manufacturers take all the aggro out of things like this by providing the fullest of information about the valve so as to make selection a simple matter.

thnx

Hi, I agree with Vulcan.Some valves have "vented" plugs, with this type of plugs the pressure is equalized on the top and bottom of the plug requiring less force to move the valve's stem

Hi all,

As stated above it is area. F=MA, i.e. Force = Mass * Area.

No more no less. This is part of actuator sizing. Try to get hold of the Fischer control valve handbook. You can download it for free from the Emmerson web site. If you read it - you will get the answers you are looking for.

You can also do a search on google for control valve actuator sizing :)

Regards,

Craig